The overall objectives of this research are to improve the performance of mammography in detecting breast cancer earlier and more accurately. This can impact favorably upon the mortality and morbidity arising from breast cancer and its treatment. Digital mammography provides a means to produce higher quality mammograms, particularly for women who have dense breasts and for whom current mammography may not be adequate. It is possible to make additional gains in the quality of mammography by improving the x-ray detector that is used to acquire the digital mammogram. These would provide more efficient use of the x rays (possible dose reduction), increased spatial resolution (sharpness) and greater precision of the diagnostic information. Our research has indicated that by combining the material, amorphous selenium, with a high resolution electronic readout device, such a detector can be made. The goal of this research is to build upon the experience, the existing laboratory resources and the preliminary results of the research group to develop this improved detector. Computer modeling will be combined with experimental measurements to predict the detailed requirements of the imaging system and to match the detector performance to these. To validate this work, a preliminary detector will be constructed by evaporation of amorphous selenium onto an existing readout device. Then, after a careful study, involving imaging physics, materials science and electronics, to further optimize the detector design, an improved readout will be produced, coated with selenium, and used to evaluate the performance of the digital mammography system employing test methods available in the laboratory. This leads to the next step of incorporating the detector into an existing clinical digital mammography system.